[TowerTalk] How critical is the 120 degree ...

[David Gilbert]

The first question seem like a rather simple vector analysis task to 
me.  Generate a simple model for the manufacturer's recommendations for 
included angles, distance from tower, and guy wire tension ... and then 
calculate the lateral force on the tower due to each guy wire.  Do the 
same analysis for the configuration under consideration (with the 
addition of translating the resulting forces to the desired directions 
of 120 degrees apart) and compare the resulting lateral forces.  Decide 
how much deviation from the spec you're willing to live with (5%? ... 
10% ... whatever) and see if it satisfies.  Keep in mind that any change 
in guy wire tension to compensate for deviations from the tower 
manufacturer's configuration needs to stay within the guy wire ratings.

Seems like a better approach to me than relying on the opinion of 
anyone, although my opinion says that when you do the calculation you 
would find that the difference between 1 degree deviation and 2 degrees 
deviation is round off error.

73,
Dave   AB7E



On 7/27/2021 12:47 AM, Jari Jussila wrote:
> Hi ...
>
> I'm sure these topics have been discussed earlier, but could not find 
> any thread ..... Sri ...
>
> We are at our club erecting two towers. A rotating steel tower being 
> 31 m high and a aluminium telescope mast 18+18 m = 32 meters.
>
>
> A) How critical is the rule that guy wires should be "exactly" 120 
> degrees apart?
> A professional guide says, that the anchor point can be 50 mm from 
> that 120 degree (119,9-120,1 degree) but some say, that a maximum of 
> two degrees is OK. That meaning 118-122 degree.
>
> What's the tower community advise?
>
>
> B) The steel tower height is 31 m - it's a rotating tower - but the 
> upper bearing is at 23 m ( leaving 8 meters for the antennas) and the 
> lower bearing at 11 meters.
>
> Whats the advise of anchor point distance? Some say, that the 60 % 
> (distance for  the tower) should be calculating from the total height 
> (31 x 0,6 = 18,6 meters).
> Some say, it should be calculating from  the upper bearing (23 m x 0,6 
> = 12.8 m)
>
> Whats your opinion?
>
> Jari, OH2BU
> For OH3AC Club Station
>